1. Field of the Invention
The present invention relates to a fixing apparatus and a fixing method for an electrophotographic apparatus.
2. Description of the Related Art
In a fixing apparatus for an electrophotographic apparatus which includes both a heat roller having heaters therein and a pressure roller urged against the heat roller, and which sandwiches and carries recording material holding a toner image on the surface thereof while heating and pressurizing the recording material at a pressing portion between the heat roller and the pressure roller, thereby to fix the toner image on the surface of the recording material, it is required to apply a constant value of heat to the toner image so as to obtain a stable fixing intensity of the toner image.
The conventional heat control system for a heat roller is arranged in the following manner (see JP-B 61-6385). For example, a temperature detecting element is provided at a portion of the outer periphery of the heat roller and a sensor head is provided so as oppose to the temperature detecting element. The temperature detecting element detects the temperature of the heat roller, and the sensor head outputs a signal when it opposes the temperature detecting element. Then, it is determined whether or not the heaters of the heat roller are to be supplied with current in accordance with the signal from the sensor head, thereby controlling the temperature of the heat roller.
In the aforesaid configuration of the conventional temperature detecting means, however, since the temperature detecting element is provided at the end portion (non-running area of a sheet) of the heat roller along the axial direction thereof, it was impossible to directly measure the temperature at the center portion (sheet running area) of the heat roller along the axial direction thereof. Accordingly, even in a case where the temperature of the sheet running area of the heat roller decreases due to the heat absorption function of the toner and the recording material (sheet etc.) and hence the temperature distribution state of the heat roller becomes as shown in FIG. 5, for example, it is impossible to detect such a state. As a consequence, it was impossible to obtain a stable fixing intensity of the toner image.